Despite what any seller might add in text to his listing eBay "real estate" auctions are not binding
You are free to walk away
http://pages.ebay.com/help/policies/non-binding-bid.html
A non-binding bid is a bid that shows a buyer's interest in purchasing an item,
but it doesn't create a formal contract between the buyer and the seller.
All bids made in the Real Estate and eBay Motors vehicles categories are considered non-binding.
Remember, bids placed in any other category are a legal commitment to purchase the item. We strongly encourage you to
read the fine print for more information.
Make sure your listing follows these guidelines. If it doesn't, you may be subject to a range of actions, including listing removal, limits on your buying and selling privileges, and suspension of your account.
Buyers shouldn't bid on an item unless they intend to buy it. However, completing the purchase may depend on things like inspections and financing. We strongly encourage sellers to include information in their listings about the requirements a buyer will need to follow (such as deposits, transfer paperwork, and transportation options) after the listing is over.
While eBay can't guarantee the completion of the sale or require members to complete a sale when a listing isn't binding, our rules require sellers and buyers to follow through with the sale in good faith.
In most cases, a bid on eBay is a legally binding contract between the buyer and the seller. Due to state laws and the complexities of real estate and vehicle transactions, bids in those categories are non-binding.
This is supported additionally buy a flat fee to list and flat fee to sell as opposed to a percentage, to stay clear of all state laws regulating the sale of real estate